Oxidation of hydrocarbons



Feb. 13-, 1940. w. H. KING ET AL OXIDATION OF HYDROCARBONS Filed 001;.30. 1936 H M m Y m .m KR m Hw A i'atented Feb. 13, 1940 UNITED STATESOXIDATION 01 HYDROOARBON William 1!. Kill, New Orleans, La., and ClydeQ. Sheely, State College, Mica; said Kin: assignor to said Shed!Application October 30, 1938, serial No. 108,478

12 Claim.

This invention relates to a new and improved process for the preparationof chemical compounds by the oxidation of aliphatic hydrocarbons andmore particularly to such a process wherein the reaction products mainlycomprise aliphatic alcohols, aldehydes and acids.

The higher aldehydes of the aliphatic series have considerable value aschemical compounds and a number of them have found use in industry asperfumes. The difficulties in the way of preparing such compounds,however, have kept their costs so high' as to limit their field ofusefulness. An improved and simpler method of obtaining such aldehydeswould make more accessible a very desirable class of products. The samecondition holds in the case of a number of the higher aliphatic alcoholsand acids also, for example those containing in the neighborhood of 8 to12 carbon atoms.

It is known that aliphatic aldehydes and acids may be obtained by theincomplete oxidation of the respective hydrocarbons by means of air oroxygen under carefully controlled conditions.

Such hydrocarbons are, as a rule, relatively inert to oxidizing agentsat temperatures low enough to prevent complete oxidation to carbondioxide and water. Methods for their partial oxidation have, however,"been disclosed by several investigators and the ,use of nitrogen oxideshas been suggested as an aid in such a process.

. Bibb, for example, in U. S. P. 1,392,886 discloses a method in whichhe utilizes a gaseous catalyst comprising nitrogen oxides to convertm'ethane into formaldehyde. Likewise James has described a process in U.S. P. 2,009,663 for converting hydrocarbons to partially oxidizedproducts, such as aldehydes and acids, by the use of various oxides, forexamples oxides of nitrogen. While such methods have been described inthe patent literature, it is not considered that their efiiciency inoperation has been suflicient to make them entirely satisfactory.

An object of our invention is an improved method for the production ofalcohols, aldehydes, and acids by the incomplete oxidation of aliphatichydrocarbons. A further object is such a process in which carefullycontrolled conditions allow a high degree of efliciency in thepreparation of the desired products. A still further object is a processin which the several products obtained may be separated in relativelypure form. Additional objects will be disclosed as the process isfurther described hereinafter.

We have found that the foregoing objects may be accomplished by theprocedure that will be detailed in the following. We introduce an excessof a normally liquid hydrocarbon in the vapor phase into a heatedchamber, into which vaporized nitric acid is conducted also. Preferablysuch nitric acid vapor will be in intimate contact with a gas containingfree oxygen, usually air, and will at least approach saturation of suchoxygen-containing gas. Within the reaction chamber, the mixed gases andvapors are subjected to a temperature between 250 and 500 C. While theoxidation of the hydrocarbons constitutes an exothermic reaction, theheat evolved will not be sufficient to obtain the desired temperatureand external heating will be necessary. It is essential that thereaction period be kept at a relatively short time interval, and we havefound 15 seconds to be the maximum allowable time. Preferably we employa reaction period not greater than 10 seconds, in order that theoxidation may not proceed too far. The reacting materials and reactionproducts are removed from the heated chamber while still in the vaporphase, and are condensed by any desired method and apparatus-under suchconditions and in such an atmosphere that further reaction cannot takeplace. 'The amount of hydrocarbon will be above the explosive limit inall cases. We have found. it desirable to use an amount of hydrocarbonin excess of 10% by volume of the gaseous reaction mixture, andpreferably between and The vaporized nitric acid is present as anoxidizing agent and not in the role of a catalyst. This agent issubstantially completely utilized during the reaction so that itsnitrogen is present in the exit products in elemental form and not asnitrogen oxides. The nitric acid is used in an amount greater than 3% byvolume of the gaseous reaction mixture. The vaporized nitric acid isintroduced, preferably as a component of a mixture with the gascontaining free oxygen, and we have found desirable concentrations ofsuch mixture to have a partial pressure of nitric acid vapor between 21and 165 mm. While the gaseous mixture in which the oxidation reactiontakes place may be at atmospheric pressure, or even slightly below, weprefer to operate at a pressure somewhat above atmospheric.

It will be a desirable step in our process also to utilize the unreactedhydrocarbon resulting from the process and to recycle it to anadditional similar oxidation step, whereby the advantages of thepresence of an excess of hydroing material.

partially saturated with nitric acid vapor and. the mixture of ,/air andsuch vapor then passes through the preheater 5. The vaporized nitricacid in air and the vaporized hydrocarbon both pass into the reactionchamber 10 where they become intimately mixed and where a tempera- 'tureof 250-500 C. is maintained, whereby partial oxidation of thehydrocarbons is brought about. The vapors pass out the pipe I! intoseparator 12, where any tar formed in the process is separated out. Themixed vapors and gases then pass through condenser l3, where theproducts capable of condensation become liquefied. The liquid condensateflows into vessel 14, while a second vessel l5 receives any furthercondensed product not caught in chamber I, but condensed in I 6. Thevessels [4 and I5 contain the liquefied unreacted hydrocarbon that haspassed through the process, and alsd'condensed water and the alcohols,aldehydes and acids resulting from the oxidation process. Such alcohols,aldehydes and acids will commonly be found in th water-insoluble layer.

Specific operating conditions suitable for our process for theproduction of alcohols, aldehydes, and acids are shown in the followingexamples. These are to be considered as merely illustrative, however,and not limiting in their application.

Example 1 v A reaction mixture comprising air containing nitric acid"vapor, in which the partial pressure of the nitric acid amounted to67.5 mm., was passed into the reaction chamber, together with the vaporsfrom an aliphatic hydrocarbon fraction having a distillation rangebetween 165 and 210 C. The hydrocarbon was present in an amount suchthat its vapor comprised about 37% of the mixture. Using a reactiontemperature of 335 C. and a contact period of 3.5 seconds, the pointyield of aldehydes, based on the amount of hydrocarbon burned, was11.54%, while the yield of acids was 91.03%. The yields are cal culatedas nonylic aldehyde and acid, respectively.

' Example 2 A reaction mixture comprising an air-nitric acid mixture,where the vapor pressure of the nitric acid was 152 mm., and vaporizedhydrocarbon of a distillation range similar to the one used in Example 1was passed into the reaction chamber at a temperature of 387 C., andmaintained there for a reaction period of 5.2 seconds. The hydrocarbonwas present in the same proportion to the air-acid mixture as inExample 1. The yields, calculated in the same manner, amounted to 12.0%aldehyde and 57.56% acid.

Example 3 A similar run using a vapor pressure of nitric acid of 67.5mm., a hydrocarbon ratio of 37.3%,

0 a temperature of 444 0., and a reaction time of as 19.73% aldenane,decane. undecane, and dodecane. The 9.1-

cohols, aldehydes, and the acids resulting from the oxidation of thesehydrocarbons are products of considerable economic value and ofdesirable properties, and the process described offers a novel andadvantageous method of obtaining such products. The alcohols, aldehydes,and acids may be separated from the hydrocarbon condensate and from oneanother by the use of suitable solvents. In the case of aldehydes, forexample, a saturated solution of sodium bisulfite was found desirablefor extraction, the bisulflte subsequently being made alkaline and beingsubjected to steam distillation. The acids were desirably extracted bymeans of .sodium hydroxide solution. The alcohols are preferablyextracted by means of phosphoric acid.

Our method, as disclosed, has been directed particularly to theoxidation of the liquid hydrocarbons by means of vaporized nitric acidin the presence of air. We have found, however, that desirable oxidationresults are obtained by the use as catalysts of such compounds astetraethyl lead, nitrobenzene, copper oleate and benzoyl peroxide,preferably in the absence of nitric acid. Such a method of operation isfavorable to the production of alcohols.

While our process has been described in detail in the foregoing, it'willbe understood that many variations in procedure may be employed withoutdeparting from the scope oi our invention. In the examples cited, ahydrocarbon fraction of a specific distillation range was used, but itwould be ahighly desirable procedure also to start with a singlealiphatic hydrocarbon, for example octane, or a, mixure of octanes.

we wish to be limited, therefore, only by the following patent claims.

We claim: I

1. The process of producing oxidation products of normally liquidaliphatic hydrocarbons, which comprises subjecting said hydrocarbons inthe vapor phase to the oxidizing action of vaporized nitric acid in agas containing free oxygen, said oxidation being carried out at atemperature between 250 and 500 C. in a reaction period not exceeding 15seconds, removing the reacting materials and the reaction products fromthe chamber while still in the vapor phase, and condensing the unreactedhydrocarbon and the oxidation products under non-reacting conditions.

2. The process of producing oxidation products of normally liquidaliphatic hydrocarbons, which comprises introducing an excess of saidhydrocarbons in the vapor phase, together with an oxidizing mediumcomprising vaporized nitric acid, into a reaction chamber at atemperature betweeen 250 and 500 C., maintaining a reaction period notexceeding 15 seconds, causing the removal of the reacting materials andthereaction products from the chamber while still in the vapor phase,and condensing the unreacted hyrocarbon and the oxidation products in anonreacting atmosphere.

3. The process for producing partially oxidized products of normallyliquid aliphatic hydrocarbons, which comprises introducing into a.reaction chamber, maintained at a temperature between 250 and500 0., anamount of said hydrocarbons in vapor state in excess of the explosivelimit, together with vaporized nitric acid and an oxygen-containing,gas, reacting said materials for a period not exceeding 15 seconds,removing the reacted materials and reaction products from the chamberwhile stillin the vapor phase, and condensing the unreacted hydrocarbonsand the oxidation products in a non-reacting atmosphere.

4. The process of claim 3 in which the nitric acid vapor is present inthe reaction chamber in an amount in excess of 3% by volume of thegaseous mixture.

5. The process of claim 3 in which the nitric acid present issubstantially completely utilized in the oxidation reaction.

6. The process of claim 3 in which the condensed oxidation productsresulting from the reaction are separated from the condensed hydrocarbonby means of suitable solvents.

7. The process of claim 3 in which the vapor phase oxidation process iscarried out under a pressure greater than atmospheric.

8. The process of claim 3 in which the unreacted hydrocarbons resultingfrom the process are re-cycled to a similar additional oxidation step.

9. The process for producing aldehydes and acids by the oxidation ofnormally liquid aliphatic hydrocarbons, which comprises subjecting, inthe vapor phase at a temperature between 250 and 500 C., hydrocarbonsfrom the group containing between 8 and 12 carbon atoms to the oxidizinaction of vaporized nitric acid, together with an oxygen-containing gas,maintaining a reaction period not exceeding 10 seconds, removing thereacting materials and reaction products from the chamber while still inthe vapor phase, condensing the unreacted hydrocarbons and the aldehydesand acids in a non-reacting atmosphere, and separating said aldehydesand acids, respectively, from the liquid condensate by extraction withsuitable solvents.

10. The process for producing aldehydes and acids according to claim 9,in which the'hydrocarbons oxidized are taken from the group consistingof octane, nonane, decane, undecane, and dodecane.

11. The process of producing as the oxidation products of normallyliquid aliphatic hydrocarbons, the corresponding aldehydes, alcohols andorganic acids, which comprises subjecting said hydrocarbons in the vaporphase to the oxidizing action of vaporized nitric acid in a gascontaining free oxygen, said oxidation being carried out at atemperature between 250 and 500 ,C. in a reaction period not exceeding15 seconds, removing from the chamber the reacting materials and thereaction products including aldehydes, alcohols and organic acids, whilestill in the vapor phase, and condensing the unreacted hydrocarbon andthe oxidation products including said aldehydes, alcohols and organicacids under nonreacting conditions.

12. The process of producing as the oxidation products of normallyliquid aliphatic hydrocarbons, the corresponding aldehydes, alcohols,and organic acids, which comprises subjecting said hydrocarbons in thevapor phase to the oxidizing action of vaporized nitric acid in a gascontaining free oxygen, said hydrocarbons being present in excess of 10%by volume of the gaseous reaction mixture, said oxidation being carriedout at a temperature between 250 and 500 C. in a reaction period notexceeding 15 seconds, removing from the chamber the reacted materialsand the reaction products including aldehydes, alcohol, and organicacids, while still in the vapor phase and condensing the unreactedhydrocarbons and oxidation products including said aldehydes, alcohols,and organic acids under nonreacting conditions, the nitric acid presentin said oxidation step being substantially completely utilized in theoxidation reaction.

WILLIAM H. KING. CLYDE Q. SHEELY.

